The present invention is directed to system and methods for recovering elemental sulfur from sulfur containing gas streams. More specifically, the present invention is directed to improvements in sulfur recovery by controllably increasing operating pressures.
A sulfur recovery unit (SRU) in a petroleum refinery converts hydrogen sulfide (H2S) to liquid elemental sulfur for further processing or storage and serves as the cleanup stage for the refineries. As available crude oil for refining gets increasingly sour, and while gasoline and diesel sulfur specifications continue to decrease due to tighter environmental regulations, an increased amount of sulfur must be processed in the refining process.
Claus sulfur recovery systems are utilized to recover sulfur from acid gas-containing sulfur plant feed stream produced in natural gas purification, gasification of solid feedstocks, and in petroleum refineries, primarily from amine sweetening. In refineries, the hydrogen sulfide is in crude oil and is contained in hydrocarbon desulfurization unit off gases and fluidized catalytic cracker unit off gases. Often times the acid gas stream produced from the amine unit is quite rich in hydrogen sulfide, particularly in petroleum refineries, where it may be 80-95 mole % hydrogen sulfide. With the known reserves of refinable hydrocarbons and crude oils decreasing, less attractive known oil reserves are now being processed, such less attractive oil reserves typically have high sulfur content. The trend in refining such high sulfur containing feedstocks may increase in the future. In refineries, an additional source of H2S that is fed to the sulfur recovery unit is generated in the sour water stripper. The sour water stripper gas stream feed to the sulfur recovery unit typically contains ⅓ H2S, ⅓ NH3 and ⅓ water vapor with trace amounts containing, but not limited to, contaminants such as CO2, phenol, light hydrocarbons. Therefore, a method for increasing the capacity of Claus plants to process sulfur is needed.
Although the foregoing discussion pertains to sulfur from oil refineries, other sources of sulfur can come from natural gas processing, gasification of solid feedstocks (such as coal, petcoke, biomass, and others) and other desulfurization operations. The concentration of hydrogen sulfide in the sulfur plant feed stream can vary from dilute (less than 50 mole %) to more than 90 mole %.
U.S. Pat. No. 4,552,747, which is hereby incorporated by reference in its entirety, discloses a method of increasing Claus plant capacity with oxygen enrichment and furnace gas recycle to moderate furnace temperatures. U.S. Pat. No. 6,508,998, which is hereby incorporated by reference in its entirety, discloses an improvement to U.S. Pat. No. 4,552,747 whereby the recycled gas is being supplied by a steam-driven eductor rather than a mechanical blower.
U.S. Pat. No. 4,632,818, which is hereby incorporated by reference in its entirety, discloses a method of increasing Claus plant capacity with oxygen enrichment and liquid sulfur recycle and injection in to the combustion zone to moderate furnace temperatures.
U.S. Pat. No. 7,597,871, which is hereby incorporated by reference in its entirety, discloses a method to increase Claus plant capacity by oxygen enrichment with steam injection to moderate furnace temperature. The steam is generated from the sulfur recovery unit 100, and may have been used previously for the eductor operation.
What is needed is a method and system for sulfur recovery that provides more efficient sulfur removal, with greater process control and does not require the capital-intensive equipment or complicated processes.